The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions and processes thereof. In one embodiment the present invention is directed to a process for the preparation of encapsulated toner compositions by a shell-forming interfacial polycondensation and a core resin-forming hydrosilylation reaction. Another specific embodiment of the present invention relates to a process for the preparation of encapsulated toner compositions comprised of a core comprised of colorants, including pigments, dyes, or mixtures thereof, and a resin obtained by hydrosilylation or polyhydrosilylation of olefins; which core is encapsulated in a polymeric shell comprised of, for example, a polyurea, a polyurethane, a polyamide, a polyester material, or mixtures thereof. In another embodiment of the present invention, there is provided a process for the preparation of an encapsulated toner composition comprised of a polymeric shell and a core comprised of colorants including pigments, dyes, mixtures thereof, and a polymer resin obtained by the reaction of a silylhydride-functionalized reagent and an olefin. In another specific embodiment of the present invention, there is provided an encapsulated toner composition wherein the core resin is comprised of a siloxane-containing polymer derived from the reaction of a silylhydride-functionalized siloxane and an olefinic compound. Examples of advantages associated with the toners and processes of the present invention include the selection of different core resins, and the utilization of a number of different colorants which are compatible with the hydrosilylation reaction. The relatively high reactivity of the hydrosilylation reaction enables the core resin forming reaction of the present invention to be accomplished at ambient temperature in some embodiments, thus reducing the energy cost associated therewith. The present process also enables a facile and effective incorporation of a desirable low surface energy siloxane material into the core resin structure without having to utilize additional release agents. With the core resin material obtained via the process of the present invention, the problem of image ghosting often observed in ionographic printing technologies is eliminated, or substantially minimized. In addition, the core resin obtained by the process of the present invention is also not leaky, that is the aforementioned core remains encapsulated and its defusion through the polymeric shell is avoided or minimized, thus eliminating or minimizing the problem of toner agglomeration associated with many encapsulated toner compositions. The core resin obtained by the process of the present invention, in some embodiments, also possesses superior surface release properties, thus permitting the use of the resulting toner compositions in imaging devices wherein a release fluid such as a silicone oil is avoided. The toner compositions obtained by the process of the present invention also display excellent powder flow characteristics and excellent toner transfer efficiency, for example over 99 percent in some embodiments from, for example, dielectric receivers or photoreceptors to paper substrate during the image development process. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. Preferably, the toner compositions of the present invention are selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide, reference U.S. Pat. No. 4,885,220 entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. The latent images are then toned with a conductive toner by inductive single component development, and are transferred and fixed simultaneously (hereafter refers to as transfix) in one single step onto paper with pressure. Specifically, the process of the present invention can be utilized to formulate toner compositions for use in commercial ionographic printer machines such as, for example, the commercially available Delphax printers including the Delphax S9000, S6000, S4500, S3000, and Xerox Corporation printers including the Xerox Corporation 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized. In another embodiment of the present invention, the toner compositions can be utilized in xerographic processes wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of photochemical or thermal energy fusing.
The toner compositions of the present invention can, in one embodiment, be prepared by first dispersing the precursor materials comprised of shell precursors, core resin precursors, colorants and hydrosilylation catalysts into stabilized microdroplets of controlled droplet size and size distribution, followed by shell formation around the microdroplets via interfacial polymerization, and subsequently generating the core polymer resin by hydrosilylation within the newly formed microcapsules. Thus, in one embodiment the present invention is directed to a process for the simple, and economical preparation of pressure fixable encapsulated toner compositions by an interfacial polymerization/hydrosilylation method wherein there are selected as the core resin precursors an olefin and a silylhydride-functionalized reagent capable of undergoing hydrosilylation with the olefin, a colorant, and a shell-forming monomer component or components capable of undergoing interfacial polymerization with another shell monomer component in the aqueous phase. Another specific embodiment of the present invention relates to the utilization of a diolefinic compound and a bis(silylhydride)-functionalized reagent as the core resin-forming precursors, the reaction of which via polyhydrosilylation enables the desired core resin. A further specific embodiment of the present invention encompasses the use of a silylhydride-, bis(silylhydride)- or poly(silylhydride)-functionalized siloxane or polysiloxane as one of the core resin-forming precursors, the reaction of which with an olefinic compound affords the desirable low surface energy siloxane-containing core resin for the toner composition of the present invention. Other process embodiments of the present invention relate to, for example, interfacial polymerization/hydrosilylation reaction processes for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention the encapsulated toners can be prepared with or without a minimum amount of organic solvent as the diluting vehicle or as a reaction medium, thus eliminating the explosion hazards associated therewith. Moreover, with the aforementioned process in an embodiment of the present invention there is obtained improved product yield per unit volume of reactor size since, for example, the extraneous solvent component can be replaced by a liquid core and shell precursors. The aforementioned toners prepared in accordance with the process of the present invention are useful for permitting the development of images in reprographic imaging systems, inclusive of electrostatic imaging processes wherein pressure fixing, especially pressure fixing in the absence of heat, is selected.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions used can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which has a tendency to severely disrupt the toner fixing characteristics of the toner selected. This can result in images of low resolution, or no images whatsoever. Also, with some of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures used. The high fixing pressure also gives rise to glossy images and objectionable paper calendering problem. Additionally, the preparative processes of the prior art pressure fixing toner compositions employed relatively large quantities of organic solvents as the reaction media, and these would drastically increase the toner's manufacturing cost because of the expensive solvent separation and recovery procedure, and the necessary precautions that have to be undertaken to prevent the solvent associated hazards. Moreover, the involvement of organic solvent in the prior art processes also decreases the product yield per unit volume of reactor size. In addition, the large amount of solvents used in many prior art processes also have deleterious effects on toner particle morphology and bulk density as a result of their removal from the toner particles during the toner isolation stage, thus causing shrinkage or collapse of the toner particles, resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention. Furthermore, with many of the prior art processes narrow size dispersity toner particles cannot be easily obtained by conventional bulk homogenization techniques as contrasted with the process of the present invention wherein narrow size dispersity toner particles are obtained. More specifically, thus with the encapsulated toners of the present invention, control of the toner physical properties of both the core and shell materials can be desirably achieved. Specifically, with the encapsulated toners of the present invention undesirable leaching or loss of core components is avoided, and image ghosting is eliminated in many instances because of the low surface energy siloxane-containing core resin illustrated herein. Image ghosting is one of the common phenomena in pressure fixing ionographic printing processes. This refers to the unwarranted repetitious generation of images, and is related to the contamination of dielectric receiver by residual toner materials which cannot be readily removed in the cleaning process. The result is the retention of some latent images on the dielectric receiver surface after cleaning, and the subsequent unwarranted development of these images. One of the common causes of image ghosting is related to the adherence of some residual toner material to the dielectric receiver during the image development process. In many of the prior art microencapsulation processes utilizing free-radical polymerization for the formation of core resin, the resultant encapsulated toners often contain residual monomers, which monomers often leach out to the toner surface causing toner agglomeration as well as image ghosting when used in pressure transfixing ionographic printing processes. The core resin forming hydrosilylation process of the present invention overcomes this disadvantage in that the core resin monomers or precursors are completely or substantially completely consumed in the formation of core resin at the very early stage of hydrosilylation, thus eliminating the above noted disadvantages.
In a patentability search report there was recited the following prior art, all United States patents: U.S. Pat. No. 4,816,366 directed to a toner obtained by suspension polymerization wherein silane coupling agents may be selected, see column 3, beginning at line 6; also note the disclosure in column 3, beginning at line 56, wherein an inorganic fine powder such as silicas is attached to the surface of polymerizable monomer composition particles to effect stabilization thereof; note the preferred process method in column 5, beginning at line 59, and examples of silicone particles that may be selected, reference column 7, and silane coupling agents, see columns 7 and 8, for example; the use of polymerizable monomers with vinyl groups is disclosed, for example, in column 12, lines 27 to 62; and crosslinking agents such as divinylbenzene may also be selected, see column 13, lines 34 to 54, for example; U.S. Pat. No. 4,465,756 directed to encapsulated toners with improved chargeability comprising a pressure fixable adhesive core material containing a colorant and a pressure rupturable shell enclosing the core material, the outer surface of the shell being provided with the surface active agent with the hydrophobic group, reference columns 3 and 4; also note specifically the disclosures in columns 5 through 9; the use of a catalyst for the formation process, reference column 5, lines 45 to 46, for example; interfacial polymerization techniques wherein there is reacted a hydrophobic liquid with a hydrophobic liquid for the purpose of forming toner shells, reference for example column 5, lines 47 to 56; U.S. Pat. No. 4,626,489 directed to a polymerizable mixture containing a monomer, a polymerization initiator and a colorant, which mixture is subjected to suspension polymerization, and wherein an additional monomer is absorbed onto the resulting polymer particles, reference the Abstract of the Disclosure; also note columns 3 to 8; the use of crosslinking agents having two or more polymerizable double bonds such as divinyl ether, reference column 3, lines 45 to 57, for example; and the use of silane coupling agents to treat magnetic material which may be incorporated into the polymerizable mixture, reference for example column 4, lines 44 to 46; and U.S. Pat. No. 4,727,011 directed to an improved process for the preparation of encapsulated toner compositions which comprises mixing in the absence of a solvent a core monomer and initiator pigment particles, a first shell monomer stabilizer in water, and accomplishing other steps including effecting a free radical polymerization of the core monomer in an interfacial polymerization reaction between a first and second shell monomer, reference the Abstract of the Disclosure, for example; note the illustrative examples of core monomers in column 6, beginning at line 21, and the examples of pigments in column 6, beginning at line 46, or examples of shell monomers are outlined, for example, in column 7, beginning at line 23. Also mentioned are U.S. Pat. Nos. 4,761,358; 3,893,933 and 4,601,968, which relate to encapsulated toners and interfacial polymerization processes in some instances.
With further reference to the prior art, there is disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization process are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Moreover, illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. Also, known encapsulated toners comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process are known.
There is illustrated in U.S. Pat. No. 5,023,159, entitled Encapsulated Toner Composition, the disclosure of this application being totally incorporated herein by reference, an encapsulated toner comprised of a core comprised of a silane modified polymer resin and pigment or dye; and a polymeric shell wherein the silane modified polymer resin has incorporated therein an oxysilyl, a dioxysilyl or a trioxysilyl, see for example Claim 1, and note, for example, claim 5 wherein specific functionalized silylenes are recited; and in U.S. Pat. No. 5,013,630, entitled Encapsulated Toner Compositions, the disclosure of which is incorporated herein by reference, there are illustrated encapsulated toners with a polysiloxane incorporated core binder.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as poly(vinyl pyrrolidone). Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Accordingly, there is a need for preparative processes and encapsulated toner compositions with many of the advantages illustrated herein. Specifically, there is a need for simple and economical processes for encapsulated toners, which permit a wide selection of shell and core resin materials. Another need resides in the provision of an interfacial polymerization/hydrosilylation process for black and colored encapsulated toner compositions comprising a hard polymeric shell and a soft core comprised of core resin and colorants, and wherein organic solvents are eliminated in their preparation in some embodiments. Another specific need is to provide encapsulated toner compositions comprising a core of a siloxane-containing core resin obtained by hydrosilylation of olefins, and colorants, and encapsulated thereover a polymeric shell coating. Also, there is a need to provide encapsulated toner compositions, including colored toners wherein image ghosting and the like is eliminated or minimized. An additional need is to provide pressure fixable encapsulated toners which offer quality images with excellent fixing levels, for example, over 70 percent at low fixing pressure of, for example, 2,000 psi. Furthermore, there is a need for encapsulated toners, including colored toners with excellent release characteristics enabling their selection in imaging systems without the use of surface release fluids such as silicone oils to prevent image offsetting to the fixing or fuser roll. Another need is to provide encapsulated toners, including colored toners with substantially no toner agglomeration, long shelf life exceeding, for example, one year, and wherein the core resin is a siloxane-containing polymer. Also, there is a need for conductive encapsulated toners that have been surface treated with additives such as carbon blacks, graphite or the like to impart to their surface certain conductive characteristics such as providing a volume resistivity of from about 1.times.10.sup.3 ohm-cm to about 1.times.10.sup.8 ohm-cm. Furthermore, there is a need for encapsulated toners wherein surface additives, such as metal salts or metal salts of fatty acids and the like, are utilized to assist in the release of the images from the imaging component to the paper substrate. There is also a need for enhanced flexibility in the design and selection of the shell and core materials for pressure fixable encapsulated toners as well as the flexibility in the control of the toner physical properties such as the bulk density, particle size, and size dispersity.